this is all very suspicious the second prince not mentioned in the novel was most likely dead in one of these explosions (saved by Leanas proposal to add more knights to the border) or he too is reincarnated and that is why things have changed so much.
Leana wants to be nice to Mia who she thinks will take the burden from her, however the Emperor is clearly falling for her. (im also curious about the retainer that suggested working outside on the same day that Mia shows up, very very suspicious)